Indole derivatives as pde5-inhibitors

ABSTRACT

Compounds of the general structural formula and use of the compounds and salts and solvates thereof, as therapeutic agents.

FIELD AND BACKGROUND OF THE INVENTION

[0001] This invention relates to a series of compounds, to methods of preparing the compounds, to pharmaceutical compositions containing the compounds, and to their use as therapeutic agents. In particular, the invention relates to compounds that are potent and selective inhibitors of cyclic guanosine 3′,5′-monophosphate specific phosphodiesterase (cGMP-specific PDE), in particular PDE5, and have utility in a variety of therapeutic areas wherein such inhibition is considered beneficial, including the treatment of cardiovascular disorders and erectile dysfunction.

DETAILED DESCRIPTION OF THE INVENTION

[0002] The present invention provides compounds of formula (I)

[0003] wherein R⁰, independently, is selected from the group consisting of halo and C₁₋₆alkyl;

[0004] R¹ is selected from the group consisting of hydrogen, C₁₋₆alkyl, C₂₋₆alkenyl, C₂₋₆alkynyl, haloC₁₋₆-alkyl, C₃₋₈cycloalkyl, C₃₋₈cycloalkylC₁₋₃alkyl, aryl-C₁₋₃alkyl, and heteroarylC₁₋₃alkyl;

[0005] R² is selected from the group consisting of an optionally substituted monocyclic aromatic ring selected from the group consisting of benzene, thiophene, furan, and pyridine, and an optionally substituted bicyclic ring

[0006] wherein the fused ring A is a 5- or 6-membered ring, saturated or partially or fully unsaturated, and comprises carbon atoms and optionally one or two heteroatoms selected from oxygen, sulfur, and nitrogen;

[0007] R³ is selected from the group consisting of hydrogen and C₁₋₃alkyl,

[0008] or R¹ and R³ together represent a 3- or 4-membered alkyl or alkenyl chain component of a 5- or 6-membered ring;

[0009] X and Y, independently, are selected from the group consisting of C(═O), SO, SO₂, C(═S), and C(R^(a))₂, and with the proviso that at least one of X and Y is different from C(═O);

[0010] R^(a) is hydrogen, C₁₋₆alkyl, or benzyl;

[0011] and q is 0, 1, 2, 3, or 4, and

[0012] pharmaceutically acceptable salts and hydrates thereof.

[0013] As used herein, the term “alkyl” includes straight chained and branched hydrocarbon groups containing the indicated number of carbon atoms, typically methyl, ethyl, and straight chain and branched propyl and butyl groups. The term “alkyl” includes “bridged alkyl,” i.e., a C₆-C₁₆ bicyclic or polycyclic hydrocarbon group, for example, norbornyl, adamantyl, bicyclo[2.2.2]octyl, bicyclo[2.2.1]-heptyl, bicyclo[3.2.1]octyl, or decahydronaphthyl. The term “cycloalkyl” is defined as a cyclic C₃-C₈ hydrocarbon group, for example, cyclopropyl, cyclobutyl, cyclohexyl, or cyclopentyl. The terms “alkenyl” and “alkynyl” are defined similarly to the term “alkyl,” except the hydrocarbon group contains a carbon-carbon double bond or carbon-carbon triple bond, respectively. “Cycloalkenyl” is defined similarly to cycloalkyl, except a carbon-carbon double bond is present in the ring. The hydrocarbon group can contain up to 16 carbon atoms.

[0014] The term “halo” or “halogen” is defined herein to include fluorine, bromine, chlorine, and iodine.

[0015] The term “haloalkyl” is defined herein as an alkyl group substituted with one or more halo substituents, either fluoro, chloro, bromo, iodo, or combinations thereof. Similarly, “halocycloalkyl” is defined as a cycloalkyl group having one or more halo substituents.

[0016] The term “aryl,” alone or in combination, is defined herein as a monocyclic or polycyclic aromatic group, preferably a monocyclic or bicyclic aromatic group, e.g., phenyl or naphthyl, that can be unsubstituted or substituted, for example, with one or more, and in particular one to three, hydroxyalkyl, alkoxy, alkoxyalkyl, haloalkyl, halo, haloalkoxy, hydroxy, alkyl, CO₂R^(a), cyano, nitro, amino, alkylamino, acylamino, alkylthio, alkylsulfinyl, and alkylsulfonyl. Exemplary aryl groups include phenyl, naphthyl, tetrahydronaphthyl, 2-chlorophenyl, 3-chlorophenyl, 4-chlorophenyl, 2-methylphenyl, 4-methoxyphenyl, 3-trifluoromethylphenyl, 4-nitrophenyl, and the like. The terms “arylC₁₋₃alkyl” and “heteroarylC₁₋₃alkyl” are defined as an aryl or heteroaryl group having a C₁₋₃alkyl substituent.

[0017] The term “heteroaryl” is defined herein as a monocyclic or bicyclic ring system containing one or two aromatic rings and containing at least one nitrogen, oxygen, or sulfur atom in an aromatic ring, and which can be unsubstituted or substituted, for example, with one or more, and in particular one to three, substituents, like halo, haloalkyl, haloalkoxy, CO₂R^(a), alkyl, hydroxy, hydroxyalkyl, alkoxy, alkoxyalkyl, haloalkyl, nitro, amino, alkylamino, acylamino, alkylthio, alkylsulfinyl, and alkylsulfonyl. Examples of heteroaryl groups include thienyl, furyl, pyridyl, oxazolyl, quinolyl, isoquinolyl, indolyl, triazolyl, isothiazolyl, isoxazolyl, imidizolyl, benzothiazolyl, pyrazinyl, pyrimidinyl, thiazolyl, and thiadiazolyl.

[0018] The term “alkoxy” is defined as —OR, wherein R is alkyl.

[0019] The term “alkoxyalkyl”, is defined as an alkyl group wherein a hydrogen has been replaced by an alkoxy group. The term “(alkylthio)alkyl” is defined similarly, except a sulfur atom, rather than an oxygen atom, is present.

[0020] The term “hydroxy” is defined as —OH.

[0021] The term “hydroxyalkyl” is defined as a hydroxy group appended to an alkyl group.

[0022] The term “amino” is defined as —NH₂, and the term “alkylamino” is defined as —NR₂, wherein at least one R is alkyl and the second R is alkyl or hydrogen.

[0023] The term “acylamino” is defined as RC(═O)N, wherein R is alkyl or aryl.

[0024] The term “alkylthio” is defined as —SR, where R is alkyl.

[0025] The term “alkylsulfinyl” is defined as R—SO₂, where R is alkyl.

[0026] The term “alkylsulfonyl” is defined as R—SO₃, where R is alkyl.

[0027] The term “nitro” is defined as —NO₂.

[0028] The term “trifluoromethyl” is defined as —CF₃.

[0029] The term “cyano” is defined as —CN.

[0030] In preferred embodiments, R² is an optionally substituted bicyclic ring system

[0031] wherein the bicyclic ring can represent, for example, naphthalene or indene, or a heterocycle, such as benzoxazole, benzothiazole, benzisoxazole, benzimidazole, quinoline, indole, benzothiophene, or benzofuran, or

[0032] wherein n is an integer 1 or 2, and X, independently, are C(R^(a))₂, O, S, or NR^(a). The bicyclic ring comprising the R² substituent typically is attached to the rest of the molecule by a phenyl ring carbon atom.

[0033] In a preferred group of compounds of formula (I), R² is represented by an optionally substituted bicyclic ring

[0034] wherein n is 1 or 2, and X, independently, are CH₂ or O. Especially preferred R¹ substituents include

[0035] Within this particular group of compounds, nonlimiting examples of substituents for the bicyclic ring include halogen (e.g., chlorine), C₁₋₃alkyl (e.g., methyl, ethyl, or i-propyl), OR^(a) (e.g., methoxy, ethoxy, or hydroxy), CO₂R^(a), halomethyl or halomethoxy (e.g., trifluoromethyl or trifluoromethoxy), cyano, nitro, and N(R^(a))₂.

[0036] An especially preferred subclass of compounds within the general scope of formula (I) is represented by compounds of formula (II)

[0037] Compounds of formula (I) can contain one or more asymmetric center, and, therefore, can exist as stereoisomers. The present invention includes both mixtures and separate individual stereoisomers of the compounds of formula (I). Compounds of formula (I) also can exist in tautomeric forms, and the invention includes both mixtures and separate individual tautomers thereof.

[0038] Pharmaceutically acceptable salts of the compounds of formula (I) can be acid addition salts formed with pharmaceutically acceptable acids. Examples of suitable salts include, but are not limited to, the hydrochloride, hydrobromide, sulfate, bisulfate, phosphate, hydrogen phosphate, acetate, benzoate, succinate, fumarate, maleate, lactate, citrate, tartrate, gluconate, methanesulfonate, benzenesulfonate, and p-toluenesulfonate salts. The compounds of the formula (I) also can provide pharmaceutically acceptable metal salts, in particular alkali metal salts and alkaline earth metal salts, with bases. Examples include the sodium, potassium, magnesium, and calcium salts.

[0039] Compounds of the present invention are potent and selective inhibitors of cGMP-specific PDE5. Thus, compounds of formula (I) are of interest for use in therapy, specifically for the treatment of a variety of conditions where selective inhibition of PDE5 is considered to be beneficial.

[0040] Phosphodiesterases (PDEs) catalyze the hydrolysis of cyclic nucleotides, such as cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). The PDEs have been classified into at least seven isoenzyme families and are present in many tissues (J. A. Beavo, Physiol. Rev., 75, p. 725 (1995)).

[0041] PDE5 inhibition is a particularly attractive target. A potent and selective inhibitor of PDE5 provides vasodilating, relaxing, and diuretic effects, all of which are beneficial in the treatment of various disease states. Research in this area has led to several classes of inhibitors based on the cGMP basic structure (E. Sybertz et al., Expert. Opin. Ther. Pat., 7, p. 631 (1997)).

[0042] The biochemical, physiological, and clinical effects of PDE5 inhibitors therefore suggest their utility in a variety of disease states in which modulation of smooth muscle, renal, hemostatic, inflammatory, and/or endocrine function is desirable. The compounds of formula (I), therefore, have utility in the treatment of a number of disorders, including stable, unstable, and variant (Prinzmetal) angina, hypertension, pulmonary hypertension, congestive heart failure, acute respiratory distress syndrome, acute and chronic renal failure, atherosclerosis, conditions of reduced blood vessel patency (e.g., postpercutaneous transluminal coronary or carotid angioplasty, or post-bypass surgery graft stenosis), peripheral vascular disease, vascular disorders, such as Raynaud's disease, thrombocythemia, inflammatory diseases, stroke, bronchitis, chronic asthma, allergic asthma, allergic rhinitis, glaucoma, osteoporosis, preterm labor, benign prostatic hypertrophy, peptic ulcer, male erectile dysfunction, female sexual dysfunction, and diseases characterized by disorders of gut motility (e.g., irritable bowel syndrome).

[0043] An especially important use is the treatment of male erectile dysfunction, which is one form of impotence and is a common medical problem. Impotence can be defined as a lack of power, in the male, to copulate, and can involve an inability to achieve penile erection or ejaculation, or both. The incidence of erectile dysfunction increases with age, with about 50% of men over the age of 40 suffering from some degree of erectile dysfunction.

[0044] In addition, a further important use is the treatment of female arousal disorder. Female arousal disorders are defined as a recurrent inability to attain or maintain an adequate lubrication/swelling response of sexual excitement until completion of sexual activity. The arousal response consists of vasocongestion in the pelvis, vaginal lubrication, and expansion and swelling of external genitalia.

[0045] It is envisioned, therefore, that compounds of formula (I) are useful in the treatment of male erectile dysfunction and female arousal disorder. Thus, the present invention concerns the use of compounds of formula (I), or a pharmaceutically acceptable salt thereof, or a pharmaceutical composition containing either entity, for the manufacture of a medicament for the curative or prophylactic treatment of erectile dysfunction in a male animal and arousal disorder in a female animal, including humans.

[0046] The term “treatment” includes preventing, lowering, stopping, or reversing the progression or severity of the condition or symptoms being treated. As such, the term “treatment” includes both medical therapeutic and/or prophylactic administration, as appropriate.

[0047] It also is understood that “a compound of formula (I),” or a physiologically acceptable salt or solvate thereof, can be administered as the neat compound, or as a pharmaceutical composition containing either entity.

[0048] Although the compounds of the invention are envisioned primarily for the treatment of sexual dysfunction in humans, such as male erectile dysfunction and female arousal disorder, they also can be used for the treatment of other disease states.

[0049] A further aspect of the present invention, therefore, is providing a compound of formula (I) for use in the treatment of stable, unstable, and variant (Prinzmetal) angina, hypertension, pulmonary hypertension, chronic obstructive pulmonary disease, congestive heart failure, acute respiratory distress syndrome, acute and chronic renal failure, atherosclerosis, conditions of reduced blood vessel patency (e.g., post-PTCA or post-bypass graft stenosis), peripheral vascular disease, vascular disorders such as Raynaud's disease, thrombocythemia, inflammatory diseases, prophylaxis of myocardial infarction, prophylaxis of stroke, stroke, bronchitis, chronic asthma, allergic asthma, allergic rhinitis, glaucoma, osteoporosis, preterm labor, benign prostatic hypertrophy, male and female erectile dysfunction, or diseases characterized by disorders of gut motility (e.g., IBS).

[0050] According to another aspect of the present invention, there is provided the use of a compound of formula (I) for the manufacture of a medicament for the treatment of the above-noted conditions and disorders.

[0051] In a further aspect, the present invention provides a method of treating the above-noted conditions and disorders in a human or nonhuman animal body which comprises administering to said body a therapeutically effective amount of a compound of formula (I).

[0052] Compounds of the invention can be administered by any suitable route, for example by oral, buccal, inhalation, sublingual, rectal, vaginal, transurethral, nasal, topical, percutaneous, i.e., transdermal, or parenteral (including intravenous, intramuscular, subcutaneous, and intracoronary) administration. Parenteral administration can be accomplished using a needle and syringe, or using a high pressure technique, like POWDERJECT™.

[0053] Oral administration of a compound of the invention is the preferred route. Oral administration is the most convenient and avoids the disadvantages associated with other routes of administration. For patients suffering from a swallowing disorder or from impairment of drug absorption after oral administration, the drug can be administered parenterally, e.g., sublingually or buccally.

[0054] Compounds and pharmaceutical compositions suitable for use in the present invention include those wherein the active ingredient is administered in an effective amount to achieve its intended purpose. More specifically, a “therapeutically effective amount” means an amount effective to prevent development of, or to alleviate the existing symptoms of, the subject being treated. Determination of the effective amounts is well within the capability of those skilled in the art, especially in light of the detailed disclosure provided herein.

[0055] A “therapeutically effective dose” refers to that amount of the compound that results in achieving the desired effect. Toxicity and therapeutic efficacy of such compounds can be determined by standard pharmaceutical procedures in cell cultures or experimental animals, e.g., for determining the-LD₅₀ (the dose lethal to 50% of the population) and the ED₅₀ (the dose therapeutically effective in 50% of the population). The dose ratio between toxic and therapeutic effects is the therapeutic index, which is expressed as the ratio between LD₅₀ and ED₅₀. Compounds which exhibit high therapeutic indices are preferred. The data obtained from such data can be used in formulating a dosage range for use in humans. The dosage of such compounds preferably lies within a range of circulating concentrations that include the ED₅₀ with little or no toxicity. The dosage can vary within this range depending upon the dosage form employed, and the route of administration utilized.

[0056] The exact formulation, route of administration, and dosage can be chosen by the individual physician in view of the patient's condition. Dosage amount and interval can be adjusted individually to provide plasma levels of the active moiety which are sufficient to maintain the therapeutic effects.

[0057] The amount of-composition administered is dependent on the subject being treated, on the subject's weight, the severity of the affliction, the manner of administration, and the judgment of the prescribing physician.

[0058] Specifically, for administration to a human in the curative or prophylactic treatment of the conditions and disorders identified above, oral dosages of a compound of formula (I) generally are about 0.5 to about 1000 mg daily for an average adult patient (70 kg). Thus, for a typical adult patient, individual tablets or capsules contain 0.2 to 500 mg of active compound, in a suitable pharmaceutically acceptable vehicle or carrier, for administration in single or multiple doses, once or several times per day. Dosages for intravenous, buccal, or sublingual administration typically are 0.1 to 500 mg per single dose as required. In practice, the physician determines the actual dosing regimen which is most suitable for an individual patient, and the dosage varies with the age, weight, and response of the particular patient. The above dosages are exemplary of the average case, but there can be individual instances in which higher or lower dosages are merited, and such are within the scope of this invention.

[0059] For human use, a compound of the formula (I) can be administered alone, but generally is administered in admixture with a pharmaceutical carrier selected with regard to the intended route of administration and standard pharmaceutical practice. Pharmaceutical compositions for use in accordance with the present invention thus can be formulated in a conventional manner using one or more physiologically acceptable carriers comprising excipients and auxiliaries that facilitate processing of compounds of formula (I) into preparations which can be used pharmaceutically.

[0060] These pharmaceutical compositions can be manufactured in a conventional manner, e.g., by conventional mixing, dissolving, granulating, dragee-making, levigating, emulsifying, encapsulating, entrapping, or lyophilizing processes. Proper formulation is dependent upon the route of administration chosen. When a therapeutically effective amount of a compound of the present invention is administered orally, the composition typically is in the form of a tablet, capsule, powder, solution, or elixir. When administered in tablet form, the composition can additionally contain a solid carrier, such as a gelatin or an adjuvant. The tablet, capsule, and powder contain about 5% to about 95% compound of the present invention, and preferably from about 25% to about 90% compound of the present invention. When administered in liquid form, a liquid carrier such as water, petroleum, or oils of animal or plant origin can be added. The liquid form of the composition can further contain physiological saline solution, dextrose or other saccharide solutions, or glycols. When administered in liquid form, the composition contains about 0.5% to about 90% by weight of a compound of the present invention, and preferably about 1% to about 50% of a compound of the present invention.

[0061] When a therapeutically effective amount of a compound of the present invention is administered by intravenous, cutaneous, or subcutaneous injection, the composition is in the form of a pyrogen-free, parenterally acceptable aqueous solution. The preparation of such parenterally acceptable solutions, having due regard to pH, isotonicity, stability, and the like, is within the skill in the art. A preferred composition for intravenous, cutaneous, or subcutaneous injection typically contains, in addition to a compound of the present invention, an isotonic vehicle.

[0062] For oral administration, the compounds can be formulated readily by combining a compound of formula (I) with pharmaceutically acceptable carriers well known in the art. Such carriers enable the present compounds to be formulated as tablets, pills, dragees, capsules, liquids, gels, syrups, slurries, suspensions and the like, for oral ingestion by a patient to be treated. Pharmaceutical preparations for oral use can be obtained by adding a compound of formula (I) with a solid excipient, optionally grinding a resulting mixture, and processing the mixture of granules, after adding suitable auxiliaries, if desired, to obtain tablets or dragee cores. Suitable excipients include, for example, fillers and cellulose preparations. If desired, disintegrating agents can be added.

[0063] For administration by inhalation, compounds of the present invention are conveniently delivered in the form of an aerosol spray presentation from pressurized packs or a nebulizer, with the use of a suitable propellant. In the case of a pressurized aerosol, the dosage unit can be determined by providing a valve to deliver a metered amount. Capsules and cartridges, e.g., gelatin, for use in an inhaler or insufflator can be formulated containing a powder mix of the compound and a suitable powder base such as lactose or starch.

[0064] The compounds can be formulated for parenteral administration by injection, e.g., by bolus injection or continuous infusion. Formulations for injection can be presented in unit dosage form, e.g., in ampules or in multidose containers, with an added preservative. The compositions can take such forms as suspensions, solutions, or emulsions in oily or aqueous vehicles, and can contain formulatory agents such as suspending, stabilizing, and/or dispersing agents.

[0065] Pharmaceutical formulations for parenteral administration include aqueous solutions of the active compounds in water-soluble form. Additionally, suspensions of the active compounds can be prepared as appropriate oily injection suspensions. Suitable lipophilic solvents or vehicles include fatty oils or synthetic fatty acid esters. Aqueous injection suspensions can contain substances which increase the viscosity of the suspension. Optionally, the suspension also can contain suitable stabilizers or agents that increase the solubility of the compounds and allow for the preparation of highly concentrated solutions. Alternatively, a present composition can be in powder form for constitution with a suitable vehicle, e.g., sterile pyrogen-free water, before use.

[0066] Compounds of the present invention also can be formulated in rectal compositions, such as suppositories or retention enemas, e.g., containing conventional suppository bases. In addition to the formulations described previously, the compounds also can be formulated as a depot preparation. Such long-acting formulations can be administered by implantation (for example, subcutaneously or intramuscularly) or by intramuscular injection. Thus, for example, the compounds can be formulated with suitable polymeric or hydrophobic materials (for example, as an emulsion in an acceptable oil) or ion exchange resins, or as sparingly soluble derivatives, for example, as a sparingly soluble salt.

[0067] Many of the compounds of the present invention can be provided as salts with pharmaceutically compatible counterions. Such pharmaceutically acceptable base addition salts are those salts that retain the biological effectiveness and properties of the free acids, and that are obtained by reaction with suitable inorganic or organic bases.

[0068] In particular, a compound of formula (I) can be administered orally, buccally, or sublingually in the form of tablets containing excipients, such as starch or lactose, or in capsules or ovules, either alone or in admixture with excipients, or in the form of elixirs or suspensions containing flavoring or coloring agents. Such liquid preparations can be prepared with pharmaceutically acceptable additives, such as suspending agents. A compound also can be injected parenterally, for example, intravenously, intramuscularly, subcutaneously, or intracoronarily. For parenteral administration, the compound is best used in the form of a sterile aqueous solution which can contain other substances, for example, salts or monosaccharides, such as mannitol or glucose, to make the solution isotonic with blood.

[0069] For veterinary use, a compound of formula (I) or a nontoxic salt thereof, is administered as a suitably acceptable formulation in accordance with normal veterinary practice. The veterinarian can readily determine the dosing regimen and route of administration that is most appropriate for a particular animal.

[0070] Thus, the invention provides in a further aspect a pharmaceutical composition comprising a compound of the formula (I), together with a pharmaceutically acceptable diluent or carrier therefor. There is further provided by the present invention a process of preparing a pharmaceutical composition comprising a compound of formula (I), which process comprises mixing a compound of formula (I), together with a pharmaceutically acceptable diluent or carrier therefor.

[0071] In a particular embodiment, the invention includes a pharmaceutical composition for the curative or prophylactic treatment of erectile dysfunction in a male animal, or arousal disorder in a female animal, including humans, comprising a compound of formula (I) or a pharmaceutically acceptable salt thereof, together with a pharmaceutically acceptable diluent or carrier.

[0072] Compounds of formula (I) can be prepared by any suitable method known in the art, or by the following processes which form part of the present invention. In the methods below, R⁰, R¹, R², and R³, as well as X and Y, are defined as in structural formula (I) above. In particular, compounds of structural formula (I) can be prepared according to the following synthetic schemes. Method A can be used to prepare compounds wherein X and/or Y are C(═S). Method B can be used to prepare compounds wherein Y is CHR^(a) and R^(a) is H, C₁₋₆alkyl, or benzyl. Methods C and D can be used to prepare compounds wherein X is CH₂. Method E can be used to prepare compounds wherein Y is SO₂.

[0073] In particular, Daugan U.S. Pat. No. 5,859,006, incorporated herein by reference, discloses preparation of a compound of structural formula (III).

[0074] In short, the compound of structural formula (III), i.e., the cis-isomer of Intermediates 1 and 2 of Daugan U.S. Pat. No. 5,859,006, was prepared according to the following reaction scheme:

[0075] A compound of structural formula (I) is prepared similarly by reacting a tryptophan ester, or a tryptophan ester substituted with suitable R⁰ substituents, with a suitable aldehyde to provide the desired R² substituent. The resulting product then is cyclized by reaction with a suitable amine to provide a compound of structural formula (I). The cyclization reaction is disclosed in Daugan U.S. Pat. No. 5,859,006.

[0076] In the synthesis of compounds of structural formula (I), protecting compounds and protecting groups, like benzyl chloroformate and trichloroethyl chloroformate, which are well known to persons skilled in the art, can be used. Such protecting groups are disclosed, for example, in T. W. Greene et al. “Protective Groups in Organic Synthesis, Third Edition,” John Wiley and Sons, Inc., NY, N.Y. (1999). These protecting groups are removed in the final steps of the synthesis under basic, acidic, or hydrogenolytic conditions which are readily apparent to those skilled in the art. By employing appropriate manipulation and protection of chemical functionalities, synthesis of compounds of structural formula (I) not specifically set forth herein can be accomplished by methods analogous to the schemes set forth below. For example, the structure of a compound of structural formula (I) can be varied by using an appropriate aldehyde to change the identity of R², or by using a halo or alkyl phenyl-substituted tryptophan ester.

[0077] Compounds of formula (I) can be converted to other compounds of formula (I). Thus, for example, when a compound contains a substituted aromatic ring, it is possible to prepare another suitably substituted compound of formula (I). Examples of appropriate interconversions include, but are not limited to, OR^(a) to hydroxy by suitable means (e.g., using an agent such as BBr₃, SnCl₂, or a palladium catalyst, such as palladium-on-carbon), or amino to substituted amino, such as alkylamine, using standard acylating or sulfonylating conditions.

[0078] Compounds of structural formula (I) can be made accordingly to one of the following five nonlimiting synthetic routes.

[0079] Method A (X and/or Y is C═S)

[0080] The 1,2,3,4-tetrahydro-β-carbolines of general formula (IV) can be prepared, for example, by the Pictet-Spengler reaction as set forth in Daugan U.S. Pat. No. 5,859,006 and in A. Madrigal et al., J. Org. Chem., 63, page 2724 (1998), for example. The resulting secondary amine then is treated with either an amino acid or an acid halide, under suitable acylation conditions, to form an amide-ester. Ring cyclization to form the diketopiperazine (V) is accomplished by intramolecular amine attack on the ester. The amine can be derived from a suitable side chain bearing a leaving group that reacts with a primary amine compound. The carbonyl groups of compound (V) thus can be converted to thiocarbonyl groups using a thionation reagent, like Lawesson's reagent. See M. P. Cava et al., Tetrahedron, 41, 5061 (1985).

[0081] Method B (Y is CHR^(a), wherein R^(a) is H, C₁₋₆alkyl, or benzyl)

[0082] The 1,2,3,4-tetrahydro-β-carboline (IV) is reacted under reductive amination conditions (see Lam, Synthesis, 135 (1975) or Abdel-Mayo, Tet. Lett., 31, 5595 (1990)) with an aldehyde or ketone having a suitable leaving group in the a-position Ring cyclization to form the amide is achieved by heating compound (VII) in a suitable solvent with a primary amine.

[0083] Method C (X═CH₂)

[0084] Compound (IV) is reduced to alcohol (VIII) using, for example, LiAlH₄ (see A. Monsees, Liebigs Ann./Recueil, 553. (1997)). Amide (IX) is formed by treatment of the secondary amine (VIII) under suitable acylation conditions with either an amino acid or an α-chloro acid halide followed by reaction with a primary amine. Ring cyclization to form the mono-keptopiperazine is accomplished by intramolecular amine attack on C-6 bearing a suitable leaving group, for example, chloride or mesylate.

[0085] Method D (X═CH₂)

[0086] Alternatively, after reduction of the ester moiety to the alcohol (VII), the alcohol (VII) can be activated using a leaving group, for example, mesylate (Xa), and can be treated with an amino acid to form (XI). Compound (XI) also can be prepared via aldehyde (Xb) and an amino acid in a reductive amination step. Coupling of the secondary amine (XI) with the carboxylic acid with DCC generated compound (I), wherein X═CH₂.

[0087] Method E (X═SO₂)

[0088] Treatment of 1,2,3,4-tetrahydro-β-carboline (IV) with chloromethanesulfonyl chloride (see L. Paquette, J. Am. Chem. Soc., 121, 8126 (1999)) under basic conditions gives Compound (XII). Reaction of sulfonamide (XII) with a primary amine gives (I) wherein Y═SO₂.

[0089] Compounds of formula (I) can be prepared by the method above as individual stereoisomers or as a racemic mixture. Individual stereoisomers of the compounds of the invention can be prepared from racemates by resolution using methods known in the art for the separation of racemic mixtures into their constituent stereoisomers, for example, using HPLC on a chiral column, such as Hypersil naphthyl urea, or using separation of salts of stereoisomers. Compounds of the invention can be isolated in association with solvent molecules by crystallization from, or evaporation of, an appropriate solvent.

[0090] The pharmaceutically acceptable acid addition salts of the compounds of formula (I) that contain a basic center can be prepared in a conventional manner. For example, a solution of the free base can be treated with a suitable acid, either neat or in a suitable solution, and the resulting salt isolated either by filtration or by evaporation under vacuum of the reaction solvent. Pharmaceutically acceptable base addition salts can be obtained in an analogous manner by treating a solution of a compound of formula (I) with a suitable base. Both types of salt can be formed or interconverted using ion-exchange resin techniques. Thus, according to a further aspect of the invention, a method for preparing a compound of formula (I) or a salt or solvate (e.g., hydrate) is provided, followed by (i) salt formation, or (ii) solvate (e.g., hydrate) formation.

[0091] The following additional abbreviations are used hereafter in the accompanying examples: rt (room temperature), min (minute), h (hour), g (gram), mmol (millimole), m.p. (melting point), eq (equivalents), L (liter), mL (milliliter), μL (microliter), CH₂Cl₂ (methylene chloride), MeOH (methanol), NaHCO₃ (sodium bicarbonate), Na₂SO₄ (sodium sulfate), NaOH (sodium hydroxide), Et₃N (triethylamine), MeNH₂ (methylamine), AcOH (acetic acid), DMSO (dimethyl sulfoxide), DCC (dicyclohexylcarbodiimide), COCl₂ (thionyl chloride), MsCl (methanesulfonyl chloride), LiAlH₄ (lithium aluminum hydride), NaB (OAc)₃H (sodium triacetoxyborohydride), NaBH₃CN (sodium cyanoborohydride), and THF (tetrahydrofuran).

PREPARATION OF EXAMPLE 1

[0092] (6R,12aR)-6-Benzo[1,3]dioxol-5-yl-2-methyl-3,4,6,7,12,12a-hexahydro-2H-pyrazino[1′,2′:1,6]pyrido[3,4-b]indole-1-one

[0093] Example 1 was prepared from the (+)-carboline (III) as depicted in the following synthetic scheme. By reducing the reaction time of the reductive amination, epimerization to the trans isomer was avoided.

[0094] Preparation of cis-2-Chloroethyl-β-carboline (Intermediate 1)

[0095] Sodium triacetoxyborohydride (4.93 g, 23.3 mmol) was added to a mixture of (+)-carboline (III) (8.14 g, 23.3 mmol), chloroacetaldehyde (2.95 mL, 23.3 mmol, 50:50 w/w in H₂O), and acetic acid (3.0 mL, 50 mmol) in CH₂Cl₂ (55 mL), and the resulting mixture was stirred at room temperature for 30 minutes. The resulting yellow suspension was diluted with CH₂Cl₂ (50 mL) and washed with water (20 mL). The organic layer was washed with saturated aqueous NaHCO₃ (2×20 mL), dried over Na₂SO₄, filtered, and the solvent was removed under reduced pressure to provide a yellow oil. The residue was purified by a quick chromatography through a short plug of silica gel, eluting with methylene chloride/ethyl acetate (25:1), to provide Intermediate 1 as a light yellow solid (2.1 g, 22%): TLC R_(f) (methylene chloride)=0.68; ¹H NMR (300 MHz, CDCl₃) δ: 7.55-7.46 (m, 1H), 7.37-7.03 (m, 4H), 6.94-6.77 (m, 3H), 5.98 (s, 1H), 5.96 (s, 1H), 5.39 (s, 1H), 3.99-3.90 (m, 1H), 3.80 (s, 3H), 3.50-3.39 (m, 1H), 3.30-2.93 (m, 5H).

PREPARATION OF EXAMPLE 1

[0096] A mixture of Intermediate 1 (824 mg, 2.0 mmol) and methylamine (6.0 mL, 2.0 M in THF, 12.0 mmol) in methanol (18 mL) was heated at 40° C. under a nitrogen blanket for 18 hours. The resulting yellow solution was concentrated under reduced pressure, and the residue was purified by flash column chromatography, eluting with methylene chloride/ethyl acetate (10:1), to provide Example 1 as a white solid (385 mg, 51%). The product was further purified by trituration with methanol (2 mL): mp 214-219° C.; TLC R_(f) (9:1 methylene chloride/ethyl acetate)=0.41; ¹H NMR (300 MHz, 43% CDCl₃ in C₆D₆) δ: 7.57-7.53 (m, 1H), 7.10-7.04 (m, 2H), 6.93-6.85 (m, 2H), 6.80 (s, 1H), 6.69-6.63 (m, 2H), 5.54 (s, 1H), 5.52 (s, 1H), 4.05 (s, 1H), 3.69 (ddd, J=15.5, 3.9, 1.5 Hz, 1H), 3.25 (dd, J=11.0, 4.1 Hz, 1H), 3.06-2.94 (m, 2H), 2.71 (s, 3H), 2.66 (dd, J=13.6, 4.1 Hz, 1H), 2.51-2.44 (m, 1H), 2.11 (dt, J=11.8, 3.6 Hz, 1H); API MS m/z 376 [C₂₂H₂₁N₃O₃+H]⁺; [α]_(D) ^(25° C.)=+67.69° (c=0.5, CHCl₃). Anal. Calcd. for C₂₂H₂₁N₃O₃-0.25H₂O: C, 69.55; H, 5.70; N, 11.06. Found: C, 69.50; H, 5.84; N, 11.08. The stereochemistry of analog Example 1 was confirmed to be the desired cis isomer by a series of NOE difference experiments: a positive NOE enhancement form the C12a proton at 3.25 ppm to the C6 proton at 4.05 ppm; a positive NOE enhancement from the C6 proton at 4.05 ppm to the C12a proton at 3.25 ppm.

PREPARATION OF EXAMPLE 2

[0097] (6S,12aR)-6-Benzo[1,3]dioxol-5-yl-2-methyl-3,4,6,7,12,12a-hexahydro-2H-pyrazino-[1′2′:1,6]pyrido[3,4-b]indol-1-one

[0098] Example 2 was prepared from Intermediate (III) as depicted in the following synthetic scheme. Under the reductive amination conditions, epimerization occurred to provide only the trans isomer.

[0099] Preparation of trans-2-Chloroethyl-β-carboline (Intermediate 2)

[0100] Sodium triacetoxyborohydride (1.91 g, 9.0 mmol) was added to a mixture of (+)-carboline (III) (2.1 g, 6.0 mmol), chloroacetaldehyde (0.84 mL, 6.6 mmol, 50/50 W/W in H₂O), acetic acid (0.39 mL, 6.6 mmol) and CH₂Cl₂ (15 mL), and the resulting mixture was stirred at room temperature for 18 hours. Additional sodium triacetoxyborohydride (1.91 g, 9.0 mmol) and chloroacetaldehyde (0.84 mL, 6.6 mmol, 50/50 w/w in H₂O) were added, and the resulting mixture was stirred at 40° C. for an additional 16 hours. The resulting yellow suspension was treated with 1 N aqueous NaOH (pH 11) and diluted with methylene chloride (70 mL). The organic layer was washed with brine, dried over Na₂SO₄₁ filtered, and the solvent was removed under reduced pressure. The residue was purified by column chromatography, eluting with CH₂Cl₂, to provide Intermediate 2 as a white solid (0.95 g, 38%). This was confirmed to be the trans isomer by NOE difference experiment (no enhancement): TLC R_(f) (CH₂Cl₂)=0.92; ¹H NMR (300 MHz, CDCl₃) δ: 7.55-7.47 (m, 1H), 7.31 (bs, 1H), 7.20-7.04 (m, 3H), 6.89 (d, J=8.6 Hz, 1H), 6.85-6.74 (m, 2H), 5.96 (s, 1H), 5.91 (s, 1H), 5.36 (s, 1H), 4.14 (t, J=4.2 Hz, 1H), 3.63 (s, 3H), 3.40-3.20 (m, 4H), 3.16-3.08 (m, 2H).

PREPARATION OF EXAMPLE 2

[0101] A mixture of Intermediate 2 (0.95 g, 2.31 mmol), methylamine (11.6 mL, 2.0 M in THF, 23.1 mmol), and methanol (20 mL) was heated at 50° C. under a nitrogen blanket for 18 hours. The resulting yellow solution was concentrated under reduced pressure, and the residue was purified by column chromatography, eluting with CH₂Cl₂/ethyl acetate (5:1), to provide Example 2 as a white solid (0.59 g, 59%). This was confirmed to be the trans isomer by NOE difference experiment (no enhancement): mp 269-275° C.; TLC R_(f) (4:1 methylene chloride/ethyl acetate)=0.23; ¹H NMR (300 MHz, DMSO-d₆) δ: 10.6 (s, 1H),-7.46 (d, J=7.5 Hz, 1H), 7.22 (d, J=7.5 Hz, 1H), 6.90-7.10 (m, 2H), 6.89-6.80 (m, 1H), 6.73 (s, 1H), 6.53 (d, J=8.1 Hz, 1H), 5.98 (s, 1H), 5.97 (s, 1H), 5.12 (s, 1H), 3.50-3.00 (m, 5H), 2.82 (s, 3H), 2.78-2.65 (m, 1H), 2.50-2.38 (m, 1H); ¹³C NMR (75 MHz, DMSO-d₆) δ: 168.5, 146.0, 146.6, 136.1, 132.9, 132.1, 126.1, 122.4, 120.8, 118.2, 117.7, 110.9, 109.5, 107.5, 106.6, 100.8, 61.2, 53.9, 47.6, 45.7, 33.4, 24.1 ppm; CI MS (methane) m/z 367 [C₂₂H₂₁N₃O₃+H]⁺; [α]_(D) ^(25° C.)=+167.4° (c=0.5, DMSO-d₆)

[0102] Anal. Calcd. for C₂₂H₂₁N₃O₃: C, 70.38; H, 5.64; N, 11.19. Found: C, 70.09; H, 5.59; N, 10.82.

PREPARATION OF EXAMPLE 3

[0103] Example 3 was prepared in a similar manner as Examples 1 and 2 using the trans isomer Intermediate (IIIa).

PREPARATION OF EXAMPLE 4

[0104] Example 4 was prepared in accordance with the synthetic sequence of Method C.

PREPARATION OF EXAMPLE 5

[0105] (6R,12aR)-6-Benzo[1,3]dioxol-5-yl-2-methyl-2,3,6,7,12,12a-hexahydropyrazino[1′,2′:1,6] pyrido[3,4-b]indole-1,4-dithione

[0106] Lawesson's reagent (3.20 g, 7.912 mmol) was added to a slurry of (6R,12aR)-6-benzo[1,3]-dioxol-5-yl-2-methyl-2,3,6,7,12,12a-hexahydropyrazino[1′,2′:1,6]pyrido[3,4-b]indole-1,4-dione (Intermediate 3, 3.00 g, 7.709 mmol) in anhydrous THF (25 mL). The synthesis of Intermediate 3 can be found in Daugan U.S. Pat. No. 5,859,006, incorporated herein by reference. The mixture was stirred at room temperature under a nitrogen blanket for 3 days. The reaction mixture was concentrated in vacuo at less than 40° C. to an orange semisolid. The product was purified by column chromatography (silica gel, CH₂Cl₂), and was recrystallized from MeOH/H₂O. Collection of the product by filtration and washing with 70% MeOH/H₂O and H₂O afforded 0.82 g (25%) of Example 5 as a pale yellow solid: mp 158-162° C.; TLC R_(f) (100% CH₂Cl₂)=0.45; ¹H NMR (300 MHz, DMSO-d₆) δ: 11.47 (s, 1H), 7.59 (d, J=7.6 Hz, 1H), 7.42 (s, 1H), 7.39 (d, J=8.0 Hz, 1H), 7.11 (td, J=1.2 Hz, J=7.0 Hz, 1H), 7.03 (td, J=1.0 Hz, J=7.4 Hz, 1H), 6.80 (d, J=8.0 Hz, 1H), 6.75 (d, J=1.7 Hz, 1H), 6.59 (dd, J=1.5 Hz, J=8.1 Hz, 1H), 5.95 (dd, J=8.7 Hz, J=1.0 Hz, 2H), 5.00 (d, J=17.1 Hz, 1H), 4.85 (d, J=18.4 Hz, 1H), 4.81 (m, 1H), 3.61 (dd, J=6.1 Hz, J=16 Hz, 1H), 3.53 (s, 3H), 3.44-3.37 (m, 1H). MS (API) m/z 420 (M−H); [α]_(D) ^(25° C.)=−531.3° (c=0.35 DMSO). Anal. Calcd. for C₂₂H₁₉N₃S₂.0.5H₂O: C, 61.37; H, 4.68; N, 9.76, S, 14.90. Found: C, 61.17; H, 4.54; N, 9.59; S, 14.98. The relative stereochemistry of the product was confirmed to be the cis isomer by NOE difference experiments (DMSO-d₆): positive NOE enhancements from the C12a proton at 4.73 ppm to the C6 proton at 7.42 ppm.

PREPARATION OF EXAMPLE 6

[0107] (6R,12aS)-6-Benzo[1,3]dioxol-5-yl-2-methyl 2,3,6,7,12,12a-hexahydropyrazino[1′,2′:1,6] pyrido[3,4-b]indole-1,4-dithione

[0108] Lawesson's reagent (3.20 g, 7.912 mmol) was added to a slurry of (6R,12aS)-6-benzo[1,3]-dioxol-5-yl-2-methyl-2,3,6,7,12,12a-hexahydropyrazino[1′,2′:1,6]pyrido[3,4-b]indole-1,4-dione (3.00 g, 7.709 mmol) in toluene (40 mL). Synthesis of the starting material can be found in Daugan U.S. Pat. No. 5,859,006. The mixture was warmed to reflux during which time an orange solution formed. No starting material was detected after 1 hour. The reaction was cooled to room temperature and concentrated in vacuo. The product was purified on silica gel using CH₂Cl₂ to elute the product. Clean fractions were combined and concentrated to a yellow solid (2.85 g). Dissolving in MeOH and adding water crystallized the product. Collection of the product by filtration and washing with 70% MeOH/H₂O and water gave 2.2 g (67%) of Example 6 as a pale yellow solid after drying at 50° C. in vacuo: mp 177-182° C.; TLC R_(f) (100% CH₂Cl₂)=0.53; ¹H NMR (300 MHz, DMSO-d₆) δ: 11.29 (s, 1H), 8.11 (s, 1H), 7.52 (d, J=7.7 Hz, 1H) 7.36 (d, J=8.0 Hz, 1H), 7.15 (t, J=7.2 Hz, 1H), 7.05 (t, J=7.3 Hz, 1H), 6.93 (d, J=8.0 Hz, 1H), 6.89 (d, J=1.4 Hz, 1H), 6.70 (dd, J=8.1 Hz, J=1.3 Hz, 1H), 6.04 (d, J=6.1 Hz, 2H), 4.96 (s, 2H), 4.73 (dd, J=4.0 Hz, J=ll.8 Hz, 1H), 3.52 (dd, J=4.1 Hz, J=15.5 Hz, 1H), 3.38 (s, 3H), 3.18 (dd, J=12.1 Hz, J=15.0 Hz, 1H); MS (API) m/z 420 (M−H); [α]_(D) ^(25° C.)=+286.4° (C=0.23, DMSO). Anal. Calcd. for C₂₂H₁₉N₃O₂S₂; C, 62.68; H, 4.54; N, 9.97; S, 15.21. Found: C, 62.22; H, 4.62; N, 9.76; S, 15.02. The relative stereochemistry of the product was confirmed to be the trans isomer by NOE difference experiments (DMSO-d₆): no NOE enhancements from the C12a proton at 4.73 ppm to the C6 proton at 8.11 ppm and a positive enhancement with a C12 proton at 3.52 ppm.

PREPARATION OF EXAMPLE 7

[0109]

[0110] Example 7 is prepared by the following synthetic sequence.

[0111] Example 8 is prepared by the synthetic sequence of Method E.

[0112] Compounds of the present invention can be formulated into tablets for oral administration. For example, a compound of formula (I) can be formed into a dispersion with a polymeric carrier by the coprecipitation method set forth in WO 96/38131, incorporated herein by reference. The coprecipitated dispersion can be blended with excipients, then pressed into tablets, which optionally are film-coated.

[0113] The compounds of structural formula (I) were tested for an ability to inhibit PDE5. The ability of a compound to inhibit PDE5 activity is related to the IC₅₀ value for the compound, i.e., the concentration of inhibitor required for 50% inhibition of enzyme activity. The IC₅₀ value for compounds of structural formula (I) were determined using recombinant human PDE5.

[0114] The compounds of the present invention typically exhibit an IC₅₀ value against recombinant human PDE5 of less than about 50 μM, and preferably less than about 25 μM, and more preferably less than about 15 μm. The compounds of the present invention typically exhibit an IC₅₀ value against recombinant human PDE5 of less than about 1 μM, and often less than about 0.05 μM. To achieve the full advantage of the present invention, a present PDE5 inhibitor has an IC₅₀ of about 0.1 nM to about 15 μM.

[0115] The production of recombinant human PDEs and the IC₅₀ determinations can be accomplished by well-known methods in the art. Exemplary methods are described as follows:

[0116] Expression Of Human PDEs

[0117] Expression in Saccharomyces cerevisiae (Yeast)

[0118] Recombinant production of human PDE1B, PDE2, PDE4A, PDE4B, PDE4C, PDE4D, PDE5, and PDE7 was carried out similarly to that described in Example 7 of U.S. Pat. No. 5,702,936, incorporated herein by reference, except that the yeast transformation vector employed, which is derived from the basic ADH2 plasmid described in Price et al., Methods in Enzymology, 185, pp. 308-318 (1990), incorporated yeast ADH2 promoter and terminator sequences and the Saccharomyces cerevisiae host was the protease-deficient strain BJ2-54 deposited on Aug. 31, 1998 with the American Type Culture Collection, Manassas, Va., under accession number ATCC 74465. Transformed host cells were grown in 2×SC-leu medium, pH 6.2, with trace metals, and vitamins. After 24 hours, YEP medium-containing glycerol was added to a final concentration of 2×YET/3% glycerol. Approximately 24 hr later, cells were harvested, washed, and stored at −70° C.

[0119] Human Phosphodiesterase Preparations

[0120] Phosphodiesterase Activity Determinations

[0121] Phosphodiesterase activity of the preparations was determined as follows. PDE assays utilizing a charcoal separation technique were performed essentially as described in Loughney et al. (1996). In this assay, PDE activity converts [32P]cAMP or [32P]cGMP to the corresponding [32P]5′-AMP or [32P]5′-GMP in proportion to the amount of PDE α-tivity present. The [32P]5′-AMP or [32P]5′-GMP then was quantitatively converted to free [32P]phosphate and unlabeled adenosine or guanosine by the action of snake venom 5′-nucleotidase. Hence, the amount of [32P]phosphate liberated is proportional to enzyme activity. The assay was performed at 30° C. in a 100 μL reaction mixture containing (final concentrations) 40 mM Tris HCl (pH 8.0), 1 μM ZnSO₄, 5 mM MgCl₂, and 0.1 mg/mL bovine serum albumin (BSA). PDE enzyme was present in quantities that yield <30% total hydrolysis of substrate (linear assay conditions). The assay was initiated by addition of substrate (1 mM [32P]cAMP or cGMP), and the mixture was incubated for 12 minutes. Seventy-five (75) μg of Crotalus atrox venom then was added, and the incubation was continued for 3 minutes (15 minutes total). The reaction was stopped by addition of 200 μL of activated charcoal (25 mg/mL suspension in 0.1 M NaH₂PO₄, pH 4). After centrifugation (750×g for 3 minutes) to sediment the charcoal, a sample of the supernatant was taken for radioactivity determination in a scintillation counter and the PDE activity was calculated.

[0122] Purification of PDE5 from S. cerevisiae

[0123] Cell pellets (29 g) were thawed on ice with an equal volume of Lysis Buffer (25 mM Tris HCl, pH 8, 5 mM MgCl₂₁ 0.25 mM DTT, 1 mM benzamidine, and 10 μM ZnSO₄). Cells were lysed in a Microfluidizer (Microfluidics Corp.) using nitrogen at 20,000 psi. The lysate was centrifuged and filtered through 0.45 μm disposable filters. The filtrate was applied to a 150 mL column of Q SEPHAROSE Fast-Flow (Pharmacia). The column was washed with 1.5 volumes of Buffer A (20 mM Bis-Tris Propane, pH 6.8, 1 mM MgCl₂₁ 0.25 mM DTT, 10 pM ZnSO₄) and eluted with a step gradient of 125 mM NaCl in Buffer A followed by a linear gradient of 125-1000 mM NaCl in Buffer A. Active fractions from the linear gradient were applied to a 180 mL hydroxyapatite column in Buffer B (20 mM Bis-Tris Propane (pH 6.8), 1 mM MgCl₂, 0.25 mM DTT, 10 μM ZnSO4, and 250 mM KCl). After loading, the column was washed with 2 volumes of Buffer B and eluted with a linear gradient of 0-125 mM potassium phosphate in Buffer B. Active fractions were pooled, precipitated with 60% ammonium sulfate, and resuspended in Buffer C (20 mM Bis-Tris Propane, pH 6.8, 125 mM NaCl, 0.5 mM DTT, and 10 μM ZnSO₄). The pool was applied to a 140 mL column of SEPHACRYL® S-300 HR and eluted with Buffer C. Active fractions were diluted to 50% glycerol and stored at −20° C.

[0124] The resultant preparations were about 85% pure by SDS-PAGE. These preparations had specific activities of about 3 μmol cGMP hydrolyzed per minute per milligram protein.

[0125] Inhibitory Effect on cGMP-PDE

[0126] cGMP-PDE activity of compounds of the present invention was measured using a one-step assay adapted from Wells et al., Biochim. Biophys. Acta, 384, 430 (1975). The reaction medium contained 50 mM Tris-HCl, pH 7.5, 5 mM magnesium acetate, 250 μg/ml 5¹-Nucleotidase, 1 mM EGTA, and 0.15 μM 8-[H³]-cGMP. Unless otherwise indicated, the enzyme used was a human recombinant PDE5 (ICOS Corp., Bothell, Washington).

[0127] Compounds of the invention were dissolved in DMSO finally present at 2% in the assay. The incubation time was 30 minutes during which the total substrate conversion did not exceed 30%.

[0128] The IC₅₀ values for the compounds examined were determined from concentration-response curves typically using concentrations ranging from 10 nM to 10 μM. Tests against other PDE enzymes using standard methodology showed that compounds of the invention are selective for the cGMP-specific PDE enzyme.

[0129] Biological Data

[0130] The compounds according to the present invention were typically found to exhibit an IC₅₀ value of less than 500 nM. An in vitro test data for representative compounds of the invention is given in the following table: TABLE 1 In vitro results Example PDE5 IC₅₀ (nM) 1 54 2 575 3 (vs. bovine aorta) 100 4 2.3 5 237 6 1,303

[0131] Obviously, many modifications and variations of the invention as hereinbefore set forth can be made without departing from the spirit and scope thereof, and, therefore, only such limitations should be imposed are indicated by the appended claims. 

What is claimed is:
 1. A compound having a formula

wherein R⁰, independently, is selected from the group consisting of halo and C₁₋₆alkyl; R¹ is selected from the group consisting of hydrogen, C₁₋₆alkyl, C₂₋₆alkenyl, C₀₋₆alkynyl, haloC₁₋₆-alkyl, C₃₋₈cycloalkyl, C₃₋₈cycloalkylC₁₋₃alkyl, aryl-C₁₋₃alkyl, and heteroarylC₁₋₃alkyl; R² is selected from the group consisting of an optionally substituted monocyclic aromatic ring selected from the group consisting of benzene, thiophene, furan, and pyridine, and an optionally substituted bicyclic ring

 wherein the fused ring A is a 5- or 6-membered ring, saturated or partially or fully unsaturated, and comprises carbon atoms and optionally one or two heteroatoms selected from oxygen, sulfur, and nitrogen; R³ is selected from the group consisting of hydrogen and C₁₋₃alkyl, or R¹ and R³ together represent a 3- or 4-membered alkyl or alkenyl chain component of a 5- or 6-membered ring; X and Y, independently, are selected from the group consisting of C(═O), SO, SO₂, C(═S), and C(R^(a))21 and with the proviso that at least one of X and Y is different from C(═O); R^(a) is hydrogen, C₁₋₆alkyl, or benzyl; and q is 0, 1, 2, 3, or 4, and pharmaceutically acceptable salts and solvates thereof.
 2. The compound of claim 1 represented by the formula

and pharmaceutically acceptable salts and solvates thereof.
 3. The compound of claim 1 wherein q is
 0. 4. The compound of claim 1 wherein R¹ is selected from the group consisting of hydrogen, C₁₋₄-alkyl, haloC₁₋₄alkyl, optionally substituted benzyl, C₃₋₆cycloalkylmethyl, pyridylC₁₋₃alkyl, and furylC₁₋₃-alkyl.
 5. The compound of claim 1 wherein R³ is hydrogen.
 6. The compound of claim 1 wherein R¹ and R³ together represent a 3- or 4-membered alkyl chain component.
 7. The compound of claim 1 wherein R² is

wherein n is an integer 1 or 2, and X, independently, is C(R^(a))₂, O, S, or NRa.
 8. The compound of claim 1 wherein R², optionally substituted, is selected from the group consisting of:


9. The compound of claim 8 wherein R² is substituted with a substituent selected from the group consisting of halogen, C₁₋₃alkyl, OR^(a), halomethyl, and halomethoxy.
 10. The compound of claim 1 wherein X and Y, independently, are selected from the group consisting of C (═S), C(R^(a))₂₁ and C(═O), with the proviso that at least one of X and Y is different from C(═O).
 11. The compound of claim 1 wherein if X is C(═O), Y is C (R^(a))₂ or SO₂.
 12. The compound of claim 1 wherein if X is C (R^(a))₂, Y is C(═O).
 13. The compound of claim 1 wherein if X is C(═S), Y is C(═S) or C═O.
 14. A compound selected from the group consisting of (6R,12aR)-6-benzo[1,3]dioxol-5-yl-2-methyl-3,4,6,7,12,12a-hexahydro-2H-pyrazino[1′,2′:1,6]pyrido[3,4-b]indol-1-one, (6S,12aR)-6-benzo-[1,3]dioxol-5-yl-2-methyl-3,4,6,7,12,12a-hexahydro-2H-pyrazino[1′,2′:1,6]pyrido[3,4-b]indol-1-one, (6R,12aR)-6-benzo[1,3]dioxol-5-yl-2-methyl-2,3,6,7,12,12a-hexahydropyrazino[1′,2′:1,6]pyrido-[3,4-b]indole-1,4-dithione, (6R,12aS)-6-benzo[1,3]-dioxol-5-yl-2-methyl-2,3,6,7,12,12a-hexahydropyrazino[1′,2′:1,6]pyrido[3,4-b]indole-1,4-dithione, and pharmaceutically acceptable salts and solvates thereof.
 15. A compound selected from the group consisting of


16. A pharmaceutical composition comprising a compound of claim 1, together with a pharmaceutically acceptable diluent or carrier.
 17. A method of treating a male or female animal for a condition where inhibition of a cGMP-specific PDE is of a therapeutic benefit comprising administering to said animal an effective amount of a pharmaceutical composition comprising a compound of claim 1, together with a pharmaceutically acceptable diluent or carrier.
 18. The method of claim 17 wherein the condition is male erectile dysfunction.
 19. The method of claim 18 wherein the treatment is an oral treatment.
 20. The method of claim 17 wherein the condition is female arousal disorder.
 21. The method of claim 20 wherein the treatment is an oral treatment.
 22. The method-of claim 17 wherein the condition is selected from the group consisting of stable angina, unstable angina, variant angina, hypertension, pulmonary hypertension, chronic obstructive pulmonary disease, malignant hypertension, pheochromocytoma, acute respiratory distress syndrome, congestive heart failure, acute renal failure, chronic renal-failure, atherosclerosis, a condition of reduced blood vessel patency, a peripheral vascular disease, a vascular disorder, thrombocythemia, an inflammatory disease, myocardial infarction, stroke, bronchitis, chronic asthma, allergic asthma, allergic rhinitis, glaucoma, peptic ulcer, a gut motility disorder, postpercutaneous transluminal coronary angioplasty, carotid angioplasty, post-bypass surgery graft stenosis, osteoporosis, preterm labor, benign prostatic hypertrophy, and irritable bowel syndrome.
 23. A method of treating a condition where inhibition of a cGMP-specific PDE is of therapeutic benefit, in a human or a nonhuman animal body, comprising administering to said body a therapeutically effective amount of a compound of claim
 1. 24. A method for the curative or prophylactic treatment of male erectile dysfunction or female arousal disorder, comprising administration of an effective dose of a compound of claim 1, and pharmaceutically acceptable salts and solvates thereof, to an animal.
 25. Use of a compound of claim 1 for the manufacture of a medicament for the curative or prophylactic treatment of a condition where inhibition of a cGMP-specific PDE is of a therapeutic benefit. 